1. Field of the Invention
The invention relates in general to methods and devices, embodiments of which include electrical contacts that are deformable into electrical continuity and hermetic sealing with an insulated wire, and, more particularly, certain embodiments of the present invention relate to electrical contact assemblies including a deformable sleeve for forming a hermetic seal between a closed barrel electrical contact and an insulated electrical wire to which the electrical contact is mounted.
2. Description of the Prior Art
Electrical contacts are conventionally provided in lieu of solder joints for purposes of providing electrical continuity between the electrically conductive core of an insulated electrical wire and an electrical bus or other device to which it is desired to attach the core. The electrically conductive cores are typically composed of some metallic material such as, for example, copper, silver, gold, aluminum, their alloys, or the like.
Electrical contacts often take a form in which a male or female contactor and a barrel are aligned generally axially along a common axis. The contactor is generally designed as either a male pin to be axially inserted into a socket, or a female socket into which a male pin is to be inserted. In either configuration, the purpose of engaging the male pin and the female socket is to complete an electrical circuit. The barrel has an axially extending cavity or tubular portion that provides an attachment location for the core of an insulated electrical wire. When the barrel is of the type described as a closed barrel, the electrical contact is typically gold plated and there is a small hole radially through the tubular wall of the barrel at approximately the bottom end of the closed axial cavity. This hole is required during the plating of the contact.
During the assembly of the electrical contact to the end of an electrical wire, the insulation is stripped from the tip of the wire to expose a short length of the electrically conductive core of the wire. The short length of exposed core is then inserted into the axial cavity in the tubular barrel of the electrical contact. The core may be either stranded or solid. The tubular wall of the barrel is typically physically crimped into electrical continuity with the bare tip of the core of the wire that is within the axial cavity. According to some previous expedients, the tubular barrel is also deformed, typically by crimping, into a hermetic seal with the insulated coating on the wire.
The tubular barrel of the closed barrel contact is open at the opposed end from the axially remote end of the contactor. The barrel and the contactor are typically formed in one piece aligned generally along a common longitudinal axis. The axially extending cavity that is formed by the tubular barrel is generally closed at the end nearest to the contactor with the radial hole at approximately this closed end.
When the wire is assembled to the electrical contact the bare tip of the core is usually inserted into the tubular barrel from the open end to substantially the full depth of the axial cavity. Previously proposed electrical contact expedients for aluminum core wire typically closed the small hole in the wall of the tubular barrel with a soft metal sleeve that was inserted into the tubular barrel during the manufacturing of the closed barrel electrical contact. The sleeve was thought to serve two purposes. It sealed this small hole and provided a soft metal to conform to the brittle aluminum core during the continuity crimp. This sleeve, however, prevents the end of the core from being visible through the hole in the wall of the barrel when the core is substantially fully inserted into the axial cavity.
When complex wiring harnesses are incorporated into a single installation, such as a large aircraft, that installation may include many thousands of electrical contacts. Such complex wiring harnesses are found, for example, in aircraft, military equipment, ships, space craft, and the like. Aluminum is a good electrical conductor, and it enjoys the advantage over most other metals of being comparatively lightweight. The use of aluminum core wire substantially reduces the weight of a large wiring harness as compared, for example, against copper core wire. Aluminum, however, corrodes easily, and it is much more brittle than some of the other metals such as, for example, copper or silver.
Where they are used, aluminum cores must be protected from corrosion to insure the reliability of the electrical connections that are made with them. Wires composed of other metals may require hermetic sealing of their cores because of exposure to corrosive environments during use. It had been previously proposed to hermetically seal the cores of wires, particularly aluminum wires, to prevent undesired corrosion. An effective hermetic seal must seal both the radial hole in the barrel of the electrical contact, and the insulation around the base of the bare tip of the core. Previously proposed sealing expedients included inserting a soft metal sleeve into the axial cavity of the barrel to cover the small opening that is at approximately the closed end of the barrel, and extending the barrel so that it surrounds the insulation that is adjacent to the bare tip of the core. The barrel is crimped at the regions of the core and the insulation for purposes of both electrical continuity and hermetic sealing, respectively. Considerable care and skill are required because there is no opportunity to directly inspect the bare tip of the core to determine whether it has been fully inserted into the axial cavity in the tubular barrel.
Electrical contact assemblies are often installed at the location where the wiring harness is or is to be mounted in some structure or vehicle. Such off-bench installations generally require the use of hand held tools, rather than bench mounted equipment. Such manually manipulated tools are used to accomplish the required electrical continuity crimping and hermetic sealing (crimp-sealed). The designs of prior electrical contacts that provided for hermetic sealing were such that the operation of manually powered crimp-seal tools required considerable skill and close attention to insure that a good crimp-seal was achieved. The inability to inspect the assembly to determine whether the tip of the core was fully inserted into the axial cavity in the hollow barrel made accurately assembling the contact to the wire a very critical operation. A bench mounted tool designed for performing both electrical continuity and hermetic crimping operations on previous electrical contacts is shown in Schwartzman US Pub. 2007/0039168, Published Feb. 22, 2007.
Typical large installations with aluminum core wire, such as large transport aircraft, use some copper core wire for particularly critical connections. As a result, at the site of the installation, there will be electrical contacts for both aluminum core and copper core wires. These contacts are not the same, and are not interchangeable. Also, the tools used to assemble the contacts to the wires are usually not the same. If a worker is not familiar with both types of contacts, or becomes confused, there is a significant risk that an electrical contact that is designed for one type of core will be assembled to a wire with a different type of core, or that the wrong tool will be used. This presents a serious safety risk. Also, the cost of inventorying and handling different types of contacts and tools for different types of cores is substantial.
Those skilled in the art have long recognized the need for an universal electrical contact or contact assembly for both, copper and aluminum wires that is inexpensive, and capable of being crimped by the identical crimping tool, and, when used with aluminum wire, is easily crimp-sealed by hand in off-bench assembly operations.
Previously proposed expedients for electrical contact systems include, for example, Peterson U.S. Pat. No. 6,814,632. FIG. 19 of this present disclosure is based on this Peterson patent. Peterson proposes providing an adhesive seal between the barrel of an electrical contact and a nonmetallic sleeve. Electrical continuity is said to be established by a crimping process, but it is not clear how Peterson proposes to obtain a seal between the insulation of a wire and the nonmetallic sleeve. As depicted in FIG. 19 to the present disclosure, Peterson proposes a nonmetallic sleeve 60, which has the same internal diameter as the hollow tubular portion 62 of the contact body 64. Sleeve 60 is adhesively joined to and extends from the hollow tubular portion 62 of the contact body. The joining is accomplished by way of an adhesive joint 66 at a joint region 68. The inner diameter of the nonmetallic sleeve 60 is such that it is prevented from sliding over the outside of the hollow tubular portion 62 of the contact body. Instead, the sleeve is proposed as an extension of the hollow tubular portion. Peterson does not suggest any solution to the problem of hermetically sealing a hole in the hollow tubular portion 62. It is not clear how the core 72 of wire 70 is sealed, if it is, unless the insulation on the wire is adhesively bonded to sleeve 60.
Another previously proposed expedient, depicted in FIG. 20 of the present disclosure, purports to be for use with aluminum core wire only. This approach proposes the use of a crimping operation to simultaneously form a continuity crimp between the bare tip of an aluminum core of an electrical wire and the contact body 80, and a hermetic seal between the skirt portion 86 and the coating of insulation on an electrical wire. Skirt portion 86 is a solid part of the contact. A soft metal insert 82 is inserted into the hollow barrel of the contact. Insert 82 hermetically seals hole 84. It also provides a soft metal interface to which the brittle aluminum core may be crimped. Insert 82 prevents direct inspection of the position of the bare tip before and after the crimping process by which electrical continuity is established between the core of the wire and the contact body. The simultaneous crimping process for both electrical continuity and hermetic sealing often requires relatively large, heavy, bench-mounted crimping devices to generate the required degree of force.
These and other difficulties of the prior art have been overcome according to the present invention.